The present invention relates to an interface board and optical transmission equipment that multiplex plural optical signals received from plural lines to transmit to a backbone network, as well as demultiplex a multiplexed optical signal received from the backbone network into individual optical signals to transmit to individual lines.
With a recent increase of traffic volume due to the growing number of broadband Internet access lines, there has been a demand to provide high-speed high-capacity networks. As a method to realize this, optical network equipment using Wavelength Division Multiplexing (WDM) technology are widely used. WDM is a technology for multiplexing optical signals of different wavelengths to a single optical fiber, able to easily realize high-capacity communication by addition of the number of wavelengths to be multiplexed without installation of new optical fibers. In recent years, networks having more flexible and various functions are desired, such as dropping and adding of any wavelengths at intermediate nodes, in addition to providing high-capacity communication. Such network transmission equipment is called Optical Add Drop Multiplexer (OADM).
Further, in recent years, signals connected to a network have been diversified according to their applications. Such signals are exemplified by Ethernet standardized by IEEE802.3, and Synchronous Digital Hierarchy/Synchronous Optical Network (SDH/SONET) standardized by ITU-T G.707 and ANSI TI.105. FIG. 1 is a list of signals to be connected to an optical network. As shown in FIG. 1, there are many types of signals to be connected to an optical network, such as SDH/SONET, GbE, 10 GbE, and Fiber Channel. Also, the transmission speeds of these signal types widely vary from 50 Mbps (bit per second) to 40 Gbps.
As described above, the optical network handles many signal types. Adoption of a different monitoring control method for each signal only makes maintenance complicated. For this reason, there has been a demand for providing a network management method independent of the signal type. A typical method for meeting such a demand is a network monitoring using an Optical Transport Network (OTN) frame standardized by ITU-T G. 709. Optical Channel (Och) frame of OTN can be mapped independent of the signal type, allowing an integrated monitoring control of the whole network. In the method using an OTN frame, fault management is possible in the OTN section by accommodating a signal to the OTN frame, adding an overhead for the OTN frame which is different from the accommodation signal, and monitoring the overhead of the OTN frame. Monitoring is also possible to determine the network section in which a failure occurs, the network between transmission equipment items or the network section of an optical signal to be accommodated. Further, long distance transmission is possible by adopting Forward Error Correction (FEC) codes.
Examples of references are as follows:
1. ITU-T G.709 Interface for the optical transport network (OTN)
2. ITU-T G. 707 Synchronous Digital Hierarchy (SDH)
3. ANSI T1.105 Synchronous Optical NETwork (SONET)
4. ANSI T11 10 Gbit Fiber Channel (10GFC)
5. IEEE standard 802.3 Information Technology—Telecommunications and information exchange between systems—Local and metropolitan area networks—Specific requirements—Carrier sense multiple access with collision detection (CSMA/CD) access method and physical layer specifications
6. IEEE standard 802.3ae Information technology—Telecommunications and information exchange between systems—Local and metropolitan area networks—Specific requirements—Part 3: Carrier sense multiple access with collision detection (CSMA/CD) access method and physical layer specifications—Media Access Control (MAC) Parameters, Physical Layer and Management Parameters for 10 Gb/s Operation
There are three transmission speeds defined in OTN: OTU (Optical Channel Transport Unit)-1 for 2.5 Gbps, OTU-2 for 10 Gbps, and OTU-3 for 40 Gbps. However, the low-speed signals with a transmission speed of less than 2.5 Gbps have not been standardized yet.
Meanwhile, because adoption of the OTN optical transmission enables integrated management of a network, mapping to the standardized OTN frame even with the transmission speed of less than 2.5 Gbps is also efficient in terms of network management. Thus, there has been adopted methods of mapping the low-speed signals with transmission speed of less than 2.5 Gbps into OTN frames originally standardized by equipment vendors. In the methods, plural signals are multiplexed in order to apply the transmission speed of less than 2.5 Gbps to the OTN frame standardized by ITU-T G. 709. Conventionally, multiplexing is realized by terminating information called a pointer (PTR) that indicates the frame position in which the first position of the virtual container is multiplexed, in order to map the input signals to the OTN frame. This makes it difficult to connect between transmission equipment items of different equipment vendors due to adoption of the vendor specific OTN frames.
FIG. 1 shows signals of different transmission speeds and frame formats. Transmission equipment includes an interface board to connect such signals to a backbone network. The interface board performs processing at an OTN signal speed corresponding to a signal type to be accommodated. Thus, in order to process plural signals, the interface board is necessary to have plural OTN function units. The OTN function units have different configurations for each signal speed, which limits the amount of hardware to be installed in the interface board. For this reason, multi-rate interface boards supporting a wide range of transmission speeds have not been realized, only allowing supporting signals with a limited range of transmission speeds, such as low-speed signals or high-speed signals.
In order to meet the traffic demand that is expected to further increase in the future, it is necessary to provide optical transmission equipment including a flexible multi-rate interface board capable of accommodating signals of different transmission speeds into the OTN frame.